The present invention relates to entangled or commingled high strength filaments and articles that include the same, particularly ballistic resistant articles.
Various constructions are known for ballistic resistant articles such as vests, curtains, mats, raincoats and umbrellas. These articles display varying degrees of resistance to penetration by high speed impact from projectiles such as BB's, bullets, shells, shrapnel, glass fragments and the like. U.S. Pat. Nos. 4,820,568; 4,748,064; 4,737,402; 4,737,401; 4,681,792; 4,650,710; 4,623,574; 4,613,535; 4,584,347; 4,563,392; 4,543,286; 4,501,856; 4,457,985; and 4,403,012 describe ballistic resistant articles which include high strength filaments made from materials such as high molecular weight extended chain polyethylene.
One type of common ballistic resistant article is a woven fabric formed from yarns of high strength filaments. For example, U.S. Pat. No. 4,858,245 broadly indicates that a plain woven, basket woven, rib woven or twill fabric can be made from high molecular weight extended chain polyethylene filament. EP-A-0 310 199 describes a ballistic resistant woven fabric consisting of high strength, ultrahigh molecular weight filaments in the weft or fill direction and a second type of filaments in the warp direction. U.S. Pat. No. 4,737,401 describes (1) a low a real density (0.1354 kg/m.sup.2) plain weave fabric having 70 ends/inch in both the warp and fill directions made from untwisted high molecular weight extended chain polyethylene yarn sized with polyvinyl alcohol, (2) a 2.times.2 basket weave fabric having 34 ends/inch and a filament areal density of 0.434 kg/m.sup.2 made from twisted (approximately 1 turn per inch ("TPI")) high molecular weight extended chain polyethylene yarn, and (3) a plain weave fabric comprised of 31 ends per inch of untwisted 1000 denier aramid yarn in both the fill and warp directions. U.S. Pat. No. 4,850,050 describes fabrics made from untwisted aramid yarn having a denier per filament (dpf) of 1.68 and 1.12, respectively. A June 1990 brochure from Akzo N.V. appears to indicate that a fabric for ballistic protection purposes could be made from a 1.33 dpf aramid yarn that is described as being "tangled".
Although these documents indicate that it might be possible to construct a ballistic resistant woven fabric from untwisted or slightly twisted yarns of high strength filaments without sizing, experience has shown that a higher amount of twist is necessary in order to obtain a commercially practical weaving performance. Increasing the amount of twist, however, tends to decrease the end use performance of the fabric, presumably for a number of reasons. First, with respect to ballistic resistance, increased twisting by definition imparts higher torsion to the yarn causing each filament to absorb the energy of an impact transverse to the running direction of the filament rather than along the stronger axial direction of the filament. High strength filaments tend to be weaker in a direction transverse to the running direction of the filament because of their poor compressive strength. Second, the yarn retains a more round shape as the twist is increased, thus preventing the yarn from flattening out to provide a more compact fabric. Third, increased twist tends to increase the denier which results in a lower cover factor. Generally, the more compact the fabric the better the ballistic performance. Moreover, there is a relatively high cost associated with twisting a finer denier yarn such as those with deniers of 500 or less.
Accordingly, a need exists for an article, particularly a fabric, that can be made efficiently and does not suffer from the above-mentioned drawbacks relating to ballistic resistance performance.